Here　we　present　a　novel　combined-strategy　of　cation　tuning　and　surface　engineering　for　the　fabrication　of　highly　active,　earth-abundant,　and　robust　two-dimensional　Ni2P　electrocatalyst.　The　nanosheets　have　lateral　sizes　of　few　hundred　nm　with　thicknesses　of　~6　nm.　Our　theoretical　calculations　suggest　the　effectiveness　of　vanadium　doping　and　oxygen　plasma,　which　do　not　only　enhance　the　density-of-state　at　Fermi　level,　but　also　make　the　Ni　sites　more　susceptible　to　OH−　adsorption.　The　oxygen　plasma　treatment　can　increase　the　wettability　of　the　catalyst　toward　KOH　solution,　improving　the　contact　angle　from　44.95°　to　16.8°　and　also　induce　a　higher　BET　surface　area;　hence,　more　active　sites　and　lower　charge　transfer　resistance　are　obtained.　As　a　result,　the　catalyst　requires　small　overpotentials　of　257　and　108　mV　to　drive　±10　mA　cm−2　alongside　with　modest　Tafel　slope　of　43.5　and　72.3　mV　dec−1　for　oxygen　evolution　reaction　and　hydrogen　evolution　reaction　in　1.0　M　KOH　solution,　respectively.　When　employed　for　overall　water　splitting,　the　catalyst　demonstrates　a　low　voltage　of　1.56　V　to　achieve　10　mA　cm−2　with　good　stability　and　durability,　outperforming　the　state-of-the-art　IrO2　||　Pt/C　which　needs　1.69　V.　This　work　opens　a　new　approach　to　engineer　low-cost　monometallic　phosphides　for　highly　efficient　water　splitting.　©　2018　Elsevier　Ltd